Tuition at Canadian universities varies by program (with engineering generally being the most expensive). International tuition rates at the big three range from:
UBC $27,700 - $33,060/yr
U of T $29,500 - $68,900/yr
McGill $18,300 - $41,800/yr
That’s Canadian dollars though so it would be cheaper in US funds. It would also be cheaper at lower tiered universities. At a school like Guelph, which while not in the same league as those three is still a respected science school, international rates are a bit lower $19,700 - $25,000. The other advantage to going to school in Canada for international students is that upon graduation they can apply for a 3 year work visa. They can also work on campus as students without a work visa.